ISO 20217-2015 pdf free download

ISO 20217-2015 pdf free download.Space data and information transfer systems Spacecraft onboard interface services File and packet store services
Systèmes de transfert des inform ations et données spatiales — Services d’interfaces a bord des véhicules spatiaux — Services de mémoirefichiers et mémoire paquets.
Writing to and reading from the packet store is always performed in sequential order, writing new packets to the tail, reading the oldest unread packets from the head, and freeing the oldest packets from the head of the queue.
Although this Recommended Practice does not exclude multiple user entities’ reading. dumping. and freeing from the packet store, it is strongly advised that only a single application should read, dump, and free from the packet store. FIFO Packet Stores can be of two forms:
Bounded. A bounded FIFO Packet Store has a defined maximum number of packets that can be stored in as queue. When the queue is full, no more packets can be added 10 the tail of the queue: packets in the Packet Store are NEVER removedldiscarded by the service in order to store new packets; instead, the user must explicitly free them. When freeing from the head of the queue. the packet is removed and a space freed up at the tail for a new packet.
— Circular. A circular FIFO Packet Store also has a defined maximum number of packets that can be stored in its queue. However, unlike the bounded F1FO Packet Store, when attempting to write to the tail of a full queue. the packet at the head of the queue, i.e., the oldest, is deleted. This kind of packet store can never run out of space to store new packets hut results in the possibility of packets being discarded by the service.
2.3.3.2 Random-Access Packet Store
In addition to the FIFO queue of a FIFO packet store, a random-access Packet Store allows selective read and delete access to stored packets. This may for example be used for payload- specific telemetry.
The logical structure of a random-access packet store is illustrated in figure 2-2. The packets in the packet store are stored in a time-stamped (see 2.3.3.2.1) FIFO queue, with a write pointer at the tail of the queue (i.e.. the newest packet), a read pointer in the queue pointing to the next packet to be read, and a free pointer at the head of the queue (i.e., the oldest packet). When a packet is written w the packet store, the packet is added to the tail of the queue and the write pointer modified to point to the packet.ISO 20217-2015 pdf free download.